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What's up with milk and radiation?

Your recent column about the safety of nuclear power also mentioned contaminated milk. But nobody explains why contamination is a big issue with milk but not with potatoes, chicken, or water. I always thought radiation was an equal-opportunity contaminant. So what's the deal with milk? -Danielle

Milk is nature's perfect radioactivity delivery system, Danielle, ideally suited to slipping nuclear contaminants into places where they can mess you up good. Let's review its many insidious advantages:

1. It's a food. While an external dusting of radionuclides isn't healthy, for efficient long-term irradiation of vulnerable organs there's no substitute for actually ingesting the stuff.

2. It's fast. Not to knock potatoes and chicken, but growing these items can take weeks or months. With milk, the fallout simply drifts over the pasture and lands on the grass, which the cows then eat. The radioactive particles are deposited in the cows' milk, the farmers milk the cows, and in a day or two the contaminated product shows up in the dairy case.

3. Because it's processed quickly, milk makes effective use of contaminants that would otherwise rapidly decay. A byproduct of uranium fission is the radioactive isotope iodine-131. Iodine is critical to functioning of the thyroid gland, and any iodine-131 consumed will be concentrated there. However, iodine-131 has a half-life of just eight days. The speed of dairying eliminates this impediment.

4. Milk also does a good job of delivering other radioactive contaminants, such as cesium-134 and cesium-137. Although not important for human health, radioactive cesium mimics potassium, which we do need, and is readily absorbed by the body. Another uranium breakdown product is strontium-90, which is especially hazardous to children, since it can be incorporated into growing bones. In contrast to radioactive iodine, strontium-90 has a half-life of about 29 years, so once it gets embedded in you, you are, as the Irish say, fooked.

5. That brings us to the most fiendish property of radioactive milk-it targets the young. Children (a) drink a lot more milk and (b) are smaller, which when you add it up means they get a much stiffer dose. Some cancers triggered by radioactivity have a long latency period; older people may die of something else first, but kids bear the full brunt.

For all these reasons, testing milk and dumping any contaminated is at the top of the list of disaster-response measures following a nuclear accident, and it's unusual, though not unknown, for bad milk to find its way into the food supply. For example:

• Iodine contamination during the 1979 Three Mile Island accident was negligible, 20 picocuries per liter. The FDA's "action level" at the time was 12,000 picocuries per liter; the current limit of 4,600 picocuries is still far in excess of what was observed.

• After the problems with the Fukushima reactors in Japan, one batch of hot milk did test at nine times the current limit, and milk and vegetable consumption was prohibited in high-risk areas. But most bans were rescinded after a couple months.

• In 1957, after a fire at the Windscale plutonium processing plant in the UK, radiation levels of 800,000 picocuries per liter and higher were found in local milk. Though contamination of milk wasn't well understood at the time, authorities figured 800,000 of anything involving curies can't be good and banned the stuff.

One last thing. We've been talking about cow's milk, but be aware that iodine-131, strontium-90, and other radioactive contaminants can also be transferred through human milk. Your best bet in that case is to stick to formula prepared before the accident, juice, or Scotch, and you might as well give some to the baby, too.